Method and system for physical layer aggregation

ABSTRACT

Aspects of a method and system for physical layer aggregation are provided. An example method includes receiving, form a medium access control (MAC) layer protocol entity, data encapsulated into a packet comprising a preamble, fragmenting said packet into a plurality of fragment payloads, and conveying each of said fragment payloads to said third portion of said one or more circuits, wherein at least one of said plurality of fragment payloads comprises one or more octets copied from said preamble.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.11/866,692, filed on Oct. 3, 2007 which, in turn, makes reference to,claims priority to, and claims the benefit of U.S. ProvisionalApplication Ser. No. 60/862,742, filed on Oct. 24, 2006, which is herebyincorporated herein by reference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to communication networks.More specifically, certain embodiments of the invention relate to amethod and system for physical layer aggregation.

BACKGROUND OF THE INVENTION

Computer networks comprise a plurality of interconnected networkingdevices, such as routers, switches and/or computers. The physicalconnection that allows one networking device to communicate with anothernetworking device is referred to as a link. Links may utilize wired orwireless communication technologies. Data may be communicated betweennetworking devices via the link in groups of binary bits referred to aspackets. The rate at which networking devices may communicate data via alink is referred to as link speed.

The task of achieving increasing link speeds is one of the challenges incomputer networking technology. Higher link speeds correspond to higherbandwidth and correspondingly higher data rates. In pursing the goal ofhigher data rates, network architects may face a number of constraints.Such higher, or “cutting edge”, data rates often require components,such as integrated circuit (IC) devices, and interconnect, such ascategory 6 (Cat6) or Cat7 cabling, which are more expensive thanequivalent, more commonly used hardware that may not be capable ofachieving the higher data rates. Thus, economic considerationspotentially represent one such constraint. Various limitations dictate aspeed at which components may operate, and a speed at which data may betransferred by the components and/or via interconnect.

As link speeds increase, one operational objective of networkingdesigners may be to incrementally control the bandwidth associated witha link so that bandwidth may be deployed within the network “on demand”.The ability to adjust link bandwidth on demand is referred to asscalability. An objective of scalability is to enable adjustment of linkbandwidth dynamically under software control, such as from an operationsadministration and maintenance (OAM) monitoring terminal.

Networks, which utilize cutting edge technologies, which enable thehigher data rates are often used to transport data that haveconsiderable value to the users of the networks, for example forexchange of financial data, or for exchange of large volumes of databetween very expensive supercomputer systems. Thus, another potentialoperational objective is to have the ability to gradually decrease thelink bandwidth in the presence of impairments that may occur on thelink. This ability to operate the link at a reduced bandwidth, ratherthan to lose use of the link altogether, is referred to as resiliency.

One approach to overcoming some of the limitations described above is tocreate a logical high bandwidth link by simultaneously transmitting thedata via a plurality of lower bandwidth physical links. This method isoften referred to as aggregation. Aggregation creates associationsbetween the logical physical link and a group of physical links. Intheory, aggregation enables scalability by increasing logical linkbandwidth by increasing the number of associated physical links. Thus,if each physical link has a bandwidth of 10 gigabits/second (Gb), ahigher speed logical link may be created by transmitting data via two 10Gb physical links. In theory, the bandwidth of this aggregated logicallink would be 20 Gb.

Aggregation also enables resiliency through gradual decreasing oflogical link bandwidth by decreasing the number of associated physicallinks. For example, a physical link, which experiences a failure, may beremoved from association with the aggregated logical link while theremaining physical links maintain association with the logical link.Thus, in a logical link associated with two 10 Gb physical links, thelogical link bandwidth may be gradually decreased by removing one of thephysical links in the association.

Link aggregation is one existing method for aggregation. A specificationfor link aggregation may be found in IEEE standard 802.3ad (IEEE802.3ad). The IEEE 802.3ad standard specifies a method for defining asingle logical link by aggregating individual physical links, eachoperating at data rates of 10 megabits/second (Mb) to 100 Mb, forexample. However, the IEEE 802.3ad link aggregation may imposelimitations on how data may be distributed among the physical linksassociated with a single logical link. This limitation may be related tothe method in which network devices communicate within the network.

When a network device A_ and network device B_ establish a communicationfor the purpose of exchanging data, the communication may be referred toas a “conversation”. The conversation may be identified by aconversation identifier, for example, network device A_ may create aconversation identifier cid=1 for the conversation with B_. Theconversation identifier enables network device A_ to establish andconcurrently maintain other conversations in addition to theconversation cid=1 by establish distinct conversation identifiers foreach conversation (for example cid=2, cid=3, . . . ).

One limitation in IEEE 802.3ad link aggregation is that packetscontaining data transmitted from a source network device (for exampleA_) to a destination network device (for example B_), associated with agiven conversation (for example cid=1), may be required to betransmitted via a single physical link, PL1, even though the logicallink, LL1, may comprise a group of physical links, PL1, PL2, PL3 andPL4, for example. In this case, the network device A_ may maintain 4concurrent conversations (for example cid=1, cid=2, cid=3 and cid=4)with the network device B_, wherein in data associated with theconversation cid=1 may be communicated via link PL1, data associatedwith the conversation cid=2 may be communicated via the link PL2, dataassociated with the conversation cid=3 may be communicated via link PL3and data associated with the conversation cid=4 may be communicated vialink PL4. However, if the network devices A_ and B_ are engaged in asingle conversation, for example the conversation cid=1, the datatransfer rate between the network devices A_ and B_ may be limited bythe bandwidth of link PL1. Thus, while the theoretical bandwidth of thelink LL1 may be equal to the sum of bandwidths of the links PL1, PL2,PL3 and PL4, the IEEE 802.3ad link aggregation may limit the bandwidthavailable for a single conversation to the bandwidth of an individuallink PL1, PL2, PL3 or PL4.

One potential reason for this limitation is that the IEEE 802.3adstandard may impose temporal ordering restrictions on packetstransferred via the logical link. These temporal ordering restrictionsmean that if the network device A_ transmits data in a sequence ofpackets P1, followed by P2, followed by P3 and followed by P4 during thecourse of a conversation, the packets must be received at the networkdevice B_ in the order P1, followed by P2, followed by P3 and followedby P4. If the packets are transmitted via the same link PL1, temporalordering may be preserved for packets transmitted from network device A_to network device B_. However, if the packets are distributed among thelinks, for example packet P1 transmitted via link PL1, packet P2transmitted via the link PL2, packet the P3 transmitted via the link PL3and the packet P4 transmitted via the link PL4, the temporal orderingcannot be guaranteed. For example, the network device B_ may receive thepackets in the following order: P1 via PL1, P3 via PL3, P2 via PL2 andP4 via PL4. Receipt of the packets in the before mentioned order mayviolate the temporal ordering restrictions which may be required forIEEE 802.3ad link aggregation.

Thus, IEEE 802.3ad link aggregation may not exhibit the property ofscalability since adding additional physical links may not result in alinear increase of logical link bandwidth due to temporal orderingrestrictions.

Within the protocol reference model (PRM) specified by the internationalorganization for standardization (ISO), the IEEE 802.3ad linkaggregation may be represented as a software entity, which is located inthe data link layer (DLL) of the PRM. Expanding further upon the DLL,the IEEE 802.3ad software entity may be represented as a linkaggregation sublayer. Relative to the link aggregation sublayer, thenext higher layer protocol entity within the DLL may be a medium accesscontrol (MAC) client. Exemplary MAC clients may comprise a bridge relayentity, or a logical link control (LLC) layer entity. Also relative tothe link aggregation sublayer, the next lower layer protocol entitywithin the DLL may be one or more instances of a MAC sublayer. There maybe a single instance of the MAC sublayer for each distinct physical linkwithin the networking device.

The link aggregation sublayer may comprise functionalities individuallyreferred to as distributor and collector. The distributor function mayoperate within a source network device while the collector function mayoperate within a destination network device. The distributor may receivepackets from the MAC client, select a MAC sublayer entity from among agroup of MAC sublayer entities associated with a logical link, and sendthe packet to the selected MAC sublayer entity. The MAC sublayer entitymay then cause the packet to be transmitted via the associated physicallink to the destination network device. The IEEE 802.3ad standard mayrequire that the distributor send packets associated with a givenconversation to a specific MAC sublayer entity due to temporal orderingrestrictions.

The collector function may receive packets from a MAC sublayer entity,M1, among a group of MAC sublayer entities. The collector may send thepacket to the MAC client. Each received packet may be associated with aconversation identifier, for example cid=1. Temporal orderingrestrictions may require that each packet containing cid=1 be receivedat the collector via the MAC sublayer entity M1.

Physical medium entity (PME) aggregation is another existing method foraggregation. A specification for PME aggregation may be found in IEEEstandard 802.3ah (IEEE 802.3ah). The IEEE 802.3ah standard specifies amethod for defining a single logical link by aggregating individualdigital subscriber line (DSL) interface links. The IEEE 802.3ah standardmay specify two interface links, which may be utilized for PMEaggregation: 10PASS-TS, a 10 Mb interface and 2BASE-TL, a 2.5 Mbinterface. For example, PME aggregation may enable defining a singlelogical link with a theoretical aggregate link bandwidth of 10 Mb byforming an association of four 2BASE-TL interface links.

Referring to the ISO PRM, the IEEE 802.3ah PME aggregation may berepresented as a hardware entity, which is located in the physical (PHY)layer. Expanding further upon the PHY layer, the IEEE 802.3ah hardwareentity may be represented as a PME aggregation sublayer. The PMEaggregation sublayer may be located within the physical coding sublayer(PCS). Within the PCS, the next higher layer protocol entity relative tothe PME aggregation sublayer may be the MAC-PHY rate matching sublayer.Relative to the PCS, the next higher layer protocol entity may be theMAC sublayer, and the next lower layer protocol entity may be the PMElayer. Relative to the MAC sublayer, the next higher layer protocolentity may be the MAC client. Each instance of a PME may correspond to aphysical interface link located within a networking device.

The PME aggregation sublayer, within the PCS sublayer, may interfacewith a plurality of PMEs. A single PME aggregation sublayer instance maycorrespond to a single logical link while the plurality of PMEs, whichinterface to the PME aggregation sublayer instance, may correspond tothe interface links that are associated with the logical link. In thisregard, the PME aggregation sublayer may enable a logical link, LL2, tocomprise a group of interface links DL1, DL2, DL3 and DL4, for example.The theoretical bandwidth of the link LL2 may be equal to the sum ofbandwidths of interface links DL1, DL2, DL3 and DL4.

Within a source networking device A_, the PME aggregation sublayerinstance may enable data associated with a conversation between thenetworking devices A_ and B_ to be distributed among the group ofinterface links associated with a single logical link. The PMEaggregation sublayer instance may receive packets sent from the MACsublayer. The packets may contain data associated with the conversationbetween networking devices A_and B_, for example. The PME aggregationsublayer may divide a data frame of each packet into a plurality offragments and distribute the fragments among the PME layer entities suchthat the plurality of fragments is transmitted via a plurality ofinterface links selected from the group of interface links associatedwith the single logical link. For example, a packet may be divided intofragments F1, F2, F3 and F4, respectively, where F1 represents the firstportion of the packet after removal of the preamble, F2 the secondportion, F3 the third portion and F4 represents the last portion of thepacket. A logical link LL2 may be formed by an association among theinterface links DL 1, DL2, DL3 and DL4. The corresponding PME entitiesmay be PM1, PM2, PM3 and PM4, respectively. The PME aggregation sublayermay send fragment F1 to PM1, F2 to PM2, F3 to PM3 and F4 to PM4.Correspondingly, PM1 may send the fragment F1 via interface link DL 1,PM2 may send the fragment F2 via DL2, PM3 may send F3 via DL3 and PM4may send F4 via DL4.

Within the destination networking device B_, the PME aggregationsublayer instance may enable reception of the fragments F1, F2, F3 andF4 from a plurality of PMEs. The PME aggregation sublayer instancewithin B_ may not place restrictions on the order in which each of thefragments is received. The PME aggregation sublayer instance mayrearrange the fragments in order F1, F2, F3 and F4 and assemble areceived packet. A completed packet may be assembled by appending apreamble field to the assembled received packet. The preamble fieldappended by the PME aggregation sublayer instance within the destinationnetworking device B_ may comprise a determined binary value, for example10101010. The appended preamble field may not comprise the same binaryvalue as did the preamble field removed by the PME aggregation sublayerinstance within the source networking device A_. Thus, the sourcenetworking device A_ may not be able to utilize the preamble field tocommunicate information, such as OAM, to the destination networkingdevice B_. The PME aggregation sublayer instance may send the completedpacket to the MAC sublayer.

The PME aggregation sublayer instance directly receives packets from theMAC-PHY rate matching sublayer. An inter packet gap (IPG) is insertedbetween packets such that after the last bit from a current packet isreceived, a time delay as defined by the IPG will elapse before the PMEaggregation sublayer instance receives the first bit from the nextpacket. The first portion of the packet may contain a preamble field.The preamble field may have a fixed length as measured in octets, forexample 8 octets. The preamble field may be utilized forsynchronization, or for other purposes, such as to communicate OAMinformation between communicating network devices.

At the source networking device, the PME aggregation sublayer instanceremoves the preamble field and copies a first portion of the packetfollowing the preamble field as a first fragment payload, FP1. Thefragment payload may have a length specified from within a range ofvalues from 64 octets to 512 octets. The PME aggregation sublayerinstance may append a first fragment header FH1 to the fragment payloadFP1. The fragment header may have a specified length, for example 2octets. A frame check sequence (FCS) may be computed and appended to FP1as a first FCS, FCS1. The collection of fields, FH1, FP1 and FCS1 form afirst fragment F1. The FCS is utilized at the destination networkingdevice to enable detection and/or correction of bit errors in a receivedfragment.

The PME aggregation sublayer instance copies a second portion of thepacket following the portion copied for FP1. The second portion becomesa second fragment payload, FP2. A second fragment F2 is generated byappending a fragment header FH2, and frame check sequence FCS2 to FP2.The PME aggregation sublayer may continue copying subsequent portions ofthe packet until the last portion has been copied. After the lastportion of the packet, FPN, has been copied a last fragment, FN, may begenerated. At this point, the packet has been fragmented.

The frame header field for each fragment, FH, contains a sequencenumber, SN, a start of packet (SOP) field and an end of packet (EOP)field. The SN field may be 14 bits in length, for example. The valuecontained in the SN field may be incremented for each subsequentfragment that is generated within the PME aggregation sublayer. Forexample, SN=1 for F1, SN=2 for F2, . . . . The SN field enables the PMEaggregation sublayer instance within the destination networking deviceto identify an order in which fragments were sent by the sourcenetworking device. The field SOP=1 for the first fragment generated froma received packet, for example F1. For fragments other than the firstfragment, SOP=0. The field EOP=1 for the last fragment generated from areceived packet, for example FN. For fragments other than the lastfragment, EOP=0.

The SOP and EOP field enable the PME aggregation sublayer instancewithin the destination networking device to identify which block offragments are associated with the same packet. For example, when thedestination PME aggregation sublayer instance receives a fragment forwhich the fragment header fields are: SN=i, SOF=1 and EOF=0, a firstfragment may be identified. Thus, a fragment for which the fragmentheader fields are: SN=i+1, SOF=0 and EOF=0 identifies a second fragmentwith at least one additional fragment to follow. A fragment for whichthe fragment header fields are: SN=i+2, SOF=0 and EOF=1 identifies athird and last fragment associated with a packet.

The IEEE 802.3ad link aggregation defines a link aggregation sublayerthat is located within the DLL in the ISO PRM. The IEEE 802.3ad linkaggregation may impose temporal ordering restrictions, which may limitscalability properties of link aggregation. The IEEE 802.3ah PMEaggregation defines a PME aggregation sublayer, which is located withinthe PHY layer in the ISO PRM. Relative to the PME aggregation sublayer,the next higher and next lower protocol layer entities may each belocated within the PHY layer.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with some aspects of the present invention asset forth in the remainder of the present application with reference tothe drawings.

BRIEF SUMMARY OF THE INVENTION

A method and system for physical layer aggregation, substantially asshown in and/or described in connection with at least one of thefigures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the presentinvention, as well as details of an illustrated embodiment thereof, willbe more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram that illustrates an exemplary protocol stack forphysical layer aggregation, in accordance with an embodiment of theinvention.

FIG. 2 is a diagram of exemplary packet fragmentation, in accordancewith an embodiment of the invention.

FIG. 3 is a diagram illustrating an exemplary distribution of fragmentsamong a plurality of physical coding sublayer entities, in accordancewith an embodiment of the invention.

FIG. 4 is a diagram of an exemplary fragment header for physical layeraggregation, in accordance with an embodiment of the invention.

FIG. 5 is a diagram of exemplary integrated circuit chip sets forphysical layer aggregation, in accordance with an embodiment of theinvention.

FIG. 6 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII, in accordance with an embodiment of theinvention.

FIG. 7 is a diagram of an exemplary protocol stack for physical layeraggregation using an XAUI, in accordance with an embodiment of theinvention.

FIG. 8 is a diagram of an exemplary protocol stack for physical layeraggregation with multi-conductor ribbon cable, in accordance with anembodiment of the invention.

FIG. 9 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII with 10GBase-T, in accordance with anembodiment of the invention.

FIG. 10 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII with 10GBase-CX4, in accordance with anembodiment of the invention.

FIG. 11 is a flowchart illustrating exemplary steps for transmittingpackets for physical layer aggregation, in accordance with an embodimentof the invention.

FIG. 12 is a flowchart illustrating exemplary steps for receivingfragments for physical layer aggregation, in accordance with anembodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain embodiments of the invention may be found in a method and systemfor physical layer aggregation. Various embodiments of the invention maycomprise an aggregation at the physical layer (APL) protocol entity,which may be located within the data link layer (DLL) or in the physical(PHY) layer. An instance of the APL protocol entity may receive packets,each of which may contain a preamble field and a frame start delimiter(FSD) field. The APL protocol entity instance may segment the contentsof each packet into a plurality of fragment payload fields. For eachfragment payload field, a fragment header field may be generated. Foreach fragment header field, a cyclical redundancy check (CRC) field maybe generated. The CRC field may enable detection and/or correction ofbinary errors in the corresponding fragment header field. Acorresponding plurality of fragments may be generated by appending thecorresponding fragment header and CRC fields to each fragment payloadfield.

Various embodiments of the invention may enable the deployment ofscalable and resilient network architectures. The plurality of fragmentsmay be sent from a source APL protocol entity instance in a sourcenetworking device to a destination APL protocol entity instance in adestination networking device via a plurality of physical links, whichmay be associated with a logical link. As the destination APL protocolentity instance receives each fragment, the CRC field in the receivedfragment may be inspected to detect and/or correct binary errors in thefragment header field. The destination APL protocol entity instance mayalso reorder received fragments based on the fragment header field tomatch the order in which the fragments were sent by the source APLprotocol entity instance. After receiving each of the fragments, thedestination APL protocol entity instance may assemble the receivedfragments to generate a packet.

FIG. 1 is a diagram that illustrates an exemplary protocol stack forphysical layer aggregation, in accordance with an embodiment of theinvention. Referring to FIG. 1, there is shown a networking device 100,a networking device 120, a logical link 140, and a plurality of physicallinks 142 a, 142 b, 144 a, 144 b, . . . , 146 a and 146 b. Thenetworking device 100 may comprise a protocol stack, which includes aMAC client entity 102, a MAC entity 104, an APL entity 106, a pluralityof PCS entities 108 a, 108 b, . . . , 108 c, a plurality of physicalmedium attachment (PMA) entities 110 a, 110 b, . . . , 110 c, and aplurality of physical medium dependent (PMD) entities 112 a, 112 b, . .. , 112 c. The networking device 120 may comprise a protocol stack,which may comprise a MAC client entity 122, a MAC entity 124, an APLentity 126, a plurality of PCS entities 128 a, 128 b, . . . , 128 c, aPMA entities 130 a, 130 b, . . . , 130 c, and a plurality of PMDentities 132 a, 132 b, . . . , 132 c.

The networking devices 100 and 120 may be communicatively coupled via aplurality of physical links. FIG. 1 illustrates an exemplary full duplexcoupling in which physical links 142 a, 144 a, . . . , and 146 a enablenetworking device 100 to communicate data to networking device 120,while physical links 142 b, 144 b, . . . , and 146 b enable networkingdevice 120 to communicate data to networking device 100. The pluralityof physical links 142 a, 142 b, 144 a, 144 b, . . . , 146 a and 146 bmay be associated with a logical link 140.

The MAC client 102 may represent a protocol entity that may eithercomprise a logical link control (LLC) entity, or a bridge entity, forexample. A description of the LLC entity may be specified in IEEE 802.2standards. A description of the bridge entity may be specified in IEEE802.1 standards. The MAC client 102 may be implemented in software,firmware and/or hardware.

The MAC entity 104 may represent a protocol entity that controls accessby the networking device 100 to the physical links 142 a, 142 b, 144 a,144 b, . . . , 146 a and 146 b. A description of the MAC entity 104 maybe specified in IEEE 802.3 standards. Two functions performed within theMAC entity 104 may include data encapsulation and medium access control.Within a source networking device, data encapsulation may comprise a setof functions that receive data to be communicated via a network, andassembles a packet by appending header fields and/or trailer fields tothe data. The packet may then be transported from a source networkingdevice to a destination networking device via the network. Within adestination networking device, data encapsulation may comprise a set offunctions that receive a packet via a network, and extract the data byparsing the packet to remove header fields and/or trailer fields. Themedium access control entity 104 may comprise a set of functions thatenable initiation of transmission of packets via the network and/orrecovery from transmission failures, such as when a packet transmittedfrom the source networking device is not successfully received by thedestination networking device.

The PCS entity may represent a protocol entity, which in a sourcenetworking device, receives packets from a higher layer protocol entityand provides logic for encoding binary data contained in packets to linecode for transmission via a physical link. An exemplary encoding methodis 64 B/66 B encoding, in which 64 bits of data may be transformed to a66 bit line code. The line code may be serialized. The PCS entity maysend the line code to a lower layer protocol entity. In a destinationnetworking device, the PCS entity may receive line code from a lowerlayer protocol entity and decode the line code to generate a packetcontaining data. The PCS entity may send the decoded packet to thehigher layer protocol entity.

Within the protocol stack shown within the networking device 100, theremay be a plurality of PCS instances corresponding to a plurality ofphysical links. For example, the PCS instance PCS 108 a may beassociated with the physical links 142 a and 142 b, the PCS instance PCS108 b may be associated with the physical links 144 a and 144 b and thePCS instance PCS 108 c may be associated with the physical links 146 aand 146 b.

The PMA entity may represent a protocol entity, which in a sourcenetworking device, receives line code from a higher layer protocolentity and provides logic performing physical medium dependent coding ofthe received line codes. The PMA entity may generate coderepresentations of the received line codes, which may be utilized forgenerating signals that may be transmitted via a physical link. The PMAentity may receive line code and generate, for example, a non-return tozero (NRZ) representation for each received line code bit. The PMAentity may also generate signal timing information. The PMA entity maysend the code representations and signal timing information to a lowerlayer protocol entity. In a destination networking device, the PMAentity may receive code representations from a lower layer protocolentity and convert the code representations, which may be based on aspecific physical medium type, to line code bits, for which therepresentations may be independent of a specific physical medium type.The destination PMA entity may recover signal timing informationreceived from the received code representations, which may be utilizedduring the line code generation process. The destination PMA entity maysend the line code to a higher layer protocol entity.

Within the protocol stack shown within the networking device 100, theremay be a plurality of PMA instances corresponding to a plurality ofphysical links. For example, the PMA instance PMA 110 a may beassociated with the physical links 142 a and 142 b, the PMA instance PMA110 b may be associated with the physical links 144 a and 144 b and thePMA instance PMA 110 c may be associated with the physical links 146 aand 146 b.

The PMD entity may represent a protocol entity, which in a sourcenetworking device, receives code representations from a higher layerprotocol entity and provides logic for generating signals that may betransmitted via a physical link. The PMD entity may receive coderepresentations and generate signals comprising voltage levels when thephysical link transmits electrical signals, or the PMD entity maygenerate signals comprising one or more optical wavelengths when thephysical link transmits optical signals. The PMD entity may send thesignals to a physical link. In a destination networking device, the PMAentity may receive electrical and/or optical signals from a physicallink and convert the signals to code representations. The destinationPMA entity may send the code representations to a higher layer protocolentity.

Within the protocol stack shown within the networking device 100, theremay be a plurality of PMD instances corresponding to a plurality ofphysical links. For example, the PMD instance PMD 112 a may beassociated with the physical links 142 a and 142 b, the PMD instance PMD112 b may be associated with the physical links 144 a and 144 b and thePMD instance PMD 112 c may be associated with the physical links 146 aand 146 b.

The physical links 142 a, 142 b, 144 a, 144 b, . . . , 146 a and 146 bmay comprise a variety of physical medium types, such as optical fiberor copper. Examples of physical link types may include 10GBASE-SR,10GBASE-LRM, 10GBASE-LR, 10GBASE-ER, 10GBASE-ZR, 10GBASE-LX4,10GBASE-CX4, 10GBASE-KX, 10GBASE-KR and 10GBASE-T, for example.

The MAC client 102 and MAC 104 protocol entities may comprisefunctionality, which may correspond to the DLL in the ISO PRM. The PCS,PMA and PMD protocol entities may comprise functionality, which maycorrespond to the PHY layer in the ISO PRM.

The APL 106 may represent a protocol entity, which may be locatedbetween the DLL and the PHY layer in a protocol stack. The APL 106 mayprovide functionality, which in a source networking device, enables apacket to be received from a higher layer protocol entity. In variousembodiments of the invention, the higher layer protocol entity may belocated within the DLL in a protocol stack. Within a source networkingdevice, the APL 106 may generate a plurality of fragment payloads,wherein each fragment payload comprises a portion of the data containedin the received packet. The APL 106 may then generate a fragment headerfor each of the fragment payloads. Each fragment header may comprise asequence number and an indication of whether the associated fragmentpayload comprises a first portion of a packet, last portion of a packet,or neither. In various embodiments of the invention, the fragmentcomprising the first portion of the packet may also contain at least aportion of a preamble when the packet contains a preamble. The binaryvalue of the preamble contained in one of more fragments may be equal tothe binary value of the preamble contained in the associated packet.Thus, in various embodiments of the invention, the preamble field fromthe packet may not be discarded when generating fragments. The APL 106may generate a CRC for each fragment header. The APL 106 may thengenerate a plurality of fragments by appending to each fragment payloada corresponding fragment header and corresponding CRC. The plurality offragments may be distributed among a plurality of lower layer protocolinstances. In various embodiments of the invention, each of the lowerlayer protocol instances may be located within the PHY layer in aprotocol stack.

Within a destination networking device, the APL 106 may receive aplurality of fragment payloads from a plurality of lower layer protocolinstances. In various embodiments of the invention, each of the lowerlayer protocol instances may be located within the PHY layer. Uponreceiving each fragment, the APL 106 may inspect the CRC field to detectand/or correct bit errors in the fragment header. The APL 106 mayinspect the fragment header to determine which portion of a receivedpacket is contained within the fragment payload. Based on the fragmentheaders, the APL 106 may determine that each of the fragments containedwithin a packet has been received when it, for example, receives: i) afragment with a fragment number, <F1>, which may comprise an indicationthat the fragment contains a first portion of a packet; ii) a fragmentwith a fragment number, <FM>, which may comprise an indication that thefragment contains a last portion of the packet; and iii) each of thefragments <F1+1>, <F1+2>, . . . , and <FM−1>. Upon receipt of the groupof fragments, the APL 106 may assemble a received packet. The APL 106may receive fragments in an arbitrary order and rearrange the order ofreceived fragments based on the contents of the fragment header. The APL106 may extract the fragment payloads from the rearranged fragments andassemble a received packet. The received packet may then be sent to ahigher layer protocol entity. In various embodiments of the invention,the higher layer protocol entity may be located within the MAC layer.

The MAC client 122 may be substantially similar to the MAC client 102.The MAC 124 may be substantially similar to the MAC 104. The APL 126 maybe substantially similar to the APL 106. The PCS 128 a, 128 b, . . . ,128 c may be substantially similar to the PCS 108 a. The PMA 130 a, 130b, . . . , 130 c may be substantially similar to the PMA 110 a. The PMD132 a, 132 b, . . . , 132 c may be substantially similar to the PMD 112a.

In operation, the networking device 100 may be a source networkingdevice in engaged in a single conversation with the networking device120, which may be a destination networking device. As the networkingdevice 100 may send data to the networking device 120. The networkingdevice 100 may utilize the logical link 140 to communicate with thenetworking device 120. Within the logical link 140, the networkingdevice 100 may utilize physical links 142 a, 144 a, . . . , and 146 a tocommunicate data to the networking device 120.

Within the networking device 100, the MAC client 102 may send a packetP1 to the MAC 104. The MAC 104 may send the packet P1 to the APL 106.The APL 106 may copy portions of the packet P1 into fragment payloads. Afragment payload FP1 may comprise a first portion of data contained inthe packet P1. The fragment payload PF1 may comprise a preamble fieldwhen the packet P1 contains a preamble. The binary value of the preamblefield copied into the fragment payload FP1 may be equal to the binaryvalue of the preamble field contained in the payload P1. A fragmentpayload FP2 may comprise a second portion of data contained in thepacket P1. A fragment payload FP3 may comprise a third portion of thedata contained in the packet P1 and FPM may comprise a final portion ofthe data contained in the packet P1.

The APL 106 may generate a fragment header for each of the fragmentpayloads. The first fragment header, FH1 may comprise a sequence number<F1> associated with the fragment payload FP1 and an indication that thefragment payload comprises the first portion of the packet P1. The APL106 may generate a CRC field, CRC1, based on the fragment header FH1.The CRC field, CRC1, may be computed based on the binary data containedin the fragment header FH1 by utilizing any of a plurality of CRCgenerator polynomials. A first fragment F1 may be generated by combiningFH1, CRC1 and FP1.

The APL 106 may also generate fragment headers for fragment payloadsFP2, FP3, . . . , and FPM. The fragment header for FP2, FH2, maycomprise a sequence number <F1+1> and an indication that the fragmentpayload FP2 contains neither a first or last portion of the packet P1. ACRC field, CRC2, may also be generated for FH2. A second fragment F2 maybe generated by combining FH2, CRC2 and FP2. The fragment header forFP3, FH3, may comprise a sequence number <F1+2> and an indication thatthe fragment payload FP3 contains neither a first or last portion of thepacket P1. A CRC field, CRC3, may also be generated for FH3. A thirdfragment F3 may be generated by combining FH3, CRC3 and FP3. Thefragment header for FPM, FHM, may comprise a sequence number <FM> and anindication that the fragment payload FPM contains a last portion of thepacket P1. A CRC field, CRCM, may also be generated for FHM. A lastfragment FM may be generated by combining FHM, CRCM and FPM.

The APL 106 may distribute the fragments among a plurality of PCSinstances in the group PCS 108 a, 108 b, . . . , and 108 c. The PCS 108a may enable data to be transmitted via the physical link 142 a, the PCS108 b may enable data to be transmitted via the physical link 144 a andthe PCS 108 c may enable data to be transmitted via the physical link146 a. By distributing the fragments among the PCS 108 a, 108 b, . . . ,and 108 c, the APL 106 may be able to exploit scalability propertiesavailable in the logical link 140 for transmission of data associatedwith a single conversation. In addition, the APL 106 may be enabled tosupport resiliency properties available in the logical link 140 byutilizing physical links, which are in an operational, non-failed state.The APL 106 may utilize a variety of criteria in selecting which PCSinstances are to receive which fragments. In an exemplary embodiment ofthe invention, the APL 106 may utilize a round robin method. In variousother exemplary embodiments of the invention, the APL 106 may utilize aload balancing method, which may attempt to make equal and/or unequalutilization of physical links associated with a logical link 140.

In an exemplary embodiment of the invention in which there may be aplurality of N PCS instances, the APL 106 may send fragment F1 to PCS108 a, fragment F2 to PCS 108 b, . . . , fragment FN to PCS108 c,fragment FN+1 to PCS 108 a, fragment FN+2 to PCS 108 b, . . . , fragmentFM−(N−1) to PCS 108 a, fragment FM−(N−2) to PCS 108 b, and fragment FMto PCS 108 c. The PCS 108 a may encode each received fragment and sendthe encoded fragments to the PMA 110 a. The PCS 108 a may send theencoded fragments to the PMA 110 a bit serially. The PMA 110 a mayconvert the bits in each encoded fragment to a NRZ representation andsend the NRZ encoded fragments to the PMD 112 a. The PMD 112 a maygenerate signals based on the NRZ encoded fragments and transmit thesignals via the physical link 142 a.

The PCS 108 b, the PMA 110 b and the PMD 112 b may operate substantiallysimilar to the PCS 108 a, the PMA 110 a and the PMD 112 a. The PMD 112 bmay transmit signals via the physical link 144 a. The PCS 108 c, PMA 110c and PMD 112 c may operate substantially similar to PCS 108 a, the PMA110 a and the PMD 112 a. The PMD 112 c may transmit signals via thephysical link 146 a.

Within the networking device 120, the PMD 132 a may receive signals viathe physical link 142 a. The PMD 132 a may convert the signals to an NRZencoded representation and send the NRZ encoded bits to the PMA 130 a.The NRZ encoded bits may be sent to the PMA 130 a bit serially. The PMA130 a may convert the NRZ encoded bit to line coded bits. The PMA 130 amay send the line coded bits to the PCS 128 a. The line coded bits maybe sent to the PCS 128 a bit serially. The PCS 128 a may collect theline coded bits and convert the line coded bits to binary data bits. ThePCS 128 a may assemble data bits to generate a received fragment, forexample received fragment F1′. The received fragment F1′ may be sent tothe APL 126.

The APL 126 may receive the fragment F1′ and inspect the CRC field,CRC1′. Based on the binary data contained in the received fragmentheader FH1′ and the received CRC field CRC′, the APL 126 may detectand/or correct bit errors in the received fragment header FH1′. Afterverifying the integrity of the fragment header, the APL 126 may inspectthe contents of the fragment header FH1′ to determine the sequencenumber and to determine which the corresponding fragment payload FP1′may contain a first portion of the packet P1, last portion, or neither.In this exemplary instance, the fragment header FH1′ may contain asequence number <F1> and an indication that the fragment payload FP1′may contain the first portion of the packet P1. The fragment payloadFP1′ may contain a preamble field. The binary value of the preamblefield contained in the fragment payload FP1″ may be equal to the binaryvalue of the preamble field in the packet P1. The APL 126 may store thereceived fragment F1′ pending receipt of additional fragments.

The PMD 132 a, PMA 130 a and PCS 128 a may receive additional signalsvia the physical link 142 a and generate subsequent fragments, which maybe sent to the APL 126. In addition, the PMD 132 b, PMA 130 b and PCS128 b may operate substantially similar to PMD 132 a, PMA 130 a and PCS128 a. The PMD 132 b may receive signals via the physical link 144 a.The PMD 132 c, PMA 130 c and PCS 128 c may operate substantially similarto PMD 132 a, PMA 130 a and PCS 128 a. The PMD 132 c may receive signalsvia the physical link 146 a.

The APL 126 may determine when it has received each of the fragmentsassociated with the packet P1 as set forth above. The APL 126 mayassemble the received fragments to generate a received packet P1′ as setforth above. The received packet P1 may be sent to the MAC 124. The MAC124 may send the received packet to the MAC client 122.

In various embodiments of the invention, the APL 106 may receive and/orsend packets from and/or to the MAC 104. Thus, to the MAC 104, theinterface to the APL 106 may be substantially similar to the interfacebetween the MAC 104 and a PHY layer protocol entity. The APL 106 maydistribute and/or receive each of a plurality of generated fragments toand/or from the lower layer protocol instances as though the fragmentswere packets. Thus, to a PHY layer protocol instance such as the PCS 108a, the interface to the APL 106 may be substantially similar to theinterface between the PHY layer protocol instance and the MAC 104. Apreamble field in the packet P1 generated by the networking device 100may be communicated to the networking device 120 via a preamble field inthe received packet P1′. Thus, in various embodiments of the invention,the preamble field may be utilized to communicate information, forexample OAM, from a source networking device to a destination networkingdevice.

In various embodiments of the invention, the maximum size of anindividual fragment payload, as measured in octets, may be configurable.For example, the maximum size of the individual fragment payload may be16 octets, and the maximum size of the individual fragment payload maybe 32 octets. The size of a fragment header, as measured in bits, mayalso be configurable, and the fragment payload size and/or fragmentheader size may be determined based on policy objectives. For example,the size of the fragment header may be 14 bits, and the fragment headersize and/or fragment payload size may be determined based on overheadconsiderations, wherein shorter fragment headers and longer fragmentpayload may result in reduced overhead. Alternatively, longer fragmentheaders may allow greater skew tolerance, where skew may be a measure ofthe difference in the propagation delay of the physical links. Otherpolicy objectives may include latency targets, and bufferingrequirements.

FIG. 2 is a diagram of exemplary packet fragmentation, in accordancewith an embodiment of the invention. Referring to FIG. 2, there is showna packet 200, inter packet gap (IPG) fields 202 and 212 and preamblefield 214. An example of the packet 200 may be the packet P1 referencein FIG. 1. The packet 200 may comprise a preamble field 204, a start offrame delimiter (SFD) 206, MAC headers and data 208, and a frame checksequence (FCS) field 210. The preamble field 204 may comprise adetermined value, for example, an alternating 10 bit pattern, or thepreamble field 204 may comprise data, for example OAM data, which isbeing communicated between a source networking device and a destinationnetworking device.

The SFD 206 may comprise a binary value, which may indicate thebeginning of the MAC headers and data field 208. The MAC headers anddata field 208 may comprise an address for the source networking deviceand/or destination networking device and data which is beingcommunicated between the two networking devices. The FCS 210 may becomputed based on the MAC headers and data field 208 and may enabledetection and correction of bit errors in the MAC headers and data field208. The IPG 202 and 212 may precede and follow the packet 200. The IPG202 may refer to a time interval between the end of transmission of aprevious packet, and the beginning of transmission of the packet 200.The IPG 212 may refer to a time interval between the end of transmissionof the packet 200, and the beginning of transmission of a succeedingpacket. The preamble 214 may be a field contained within the succeedingpacket.

Also shown in FIG. 2 is an exemplary segmentation of the data containedin the packet 200 into fragment payloads 220 a, 220 b, 220 c . . . , and220 d. The fragment payload 220 a may comprise a first portion of thepacket 200. The fragment payload 220 a may comprise the preamble field204 from the packet 200. An exemplary fragment payload 220 a may be thefragment payload FP1 described in FIG. 1. The fragment payload 220 b maycomprise a second portion of the packet 200. An exemplary fragmentpayload 220 b may be the fragment payload FP2 described in FIG. 1. Thefragment payload 220 c may comprise a third portion of the packet 200.An exemplary fragment payload 220 c may be the fragment payload FP3described in FIG. 1. The fragment payload 220 d may comprise a lastportion of the packet 200. An exemplary fragment payload 220 d may bethe fragment payload FPM described in FIG. 1.

FIG. 3 is a diagram illustrating an exemplary distribution of fragmentsamong a plurality of physical coding sublayer entities, in accordancewith an embodiment of the invention. Referring to FIG. 3, there is showna plurality of fragments 300 a, 300 b, 300 c, . . . , 300 d, . . . , and300 e. Also shown is a plurality of fragment headers 302 a, 304 a, 306a, 308 a, . . . , 312 a, 314 a, 316 a, . . . , and 318 a, a plurality ofCRC fields 302 b, 304 b, 306 b, 308 b, 312 b, 314 b, 316 b, . . . , and318 b. Also shown is a plurality of fragment payloads 220 a, 220 b, 220c, . . . , 308 c, . . . , 312 c, 314 c, 316 c, . . . , and 220 d.

The APL 106 may generate fragment 300 a by combining fragment header 302a, CRC 302 b and fragment payload 220 a. An exemplary fragment 300 a maybe fragment F1 described in FIG. 1. An exemplary fragment header 302 amay be fragment header FH1 described in FIG. 1. An exemplary CRC field302 b may be CRC1 described in FIG. 1.

The APL 106 may generate fragment 300 b by combining fragment header 304a, CRC 304 b and fragment payload 220 b. An exemplary fragment 300 b maybe fragment F2 described in FIG. 1. An exemplary fragment header 304 amay be fragment header FH2 described in FIG. 1. An exemplary CRC field304 b may be CRC2 described in FIG. 1.

The APL 106 may generate fragment 300 c by combining fragment header 306a, CRC 306 b and fragment payload 220 c. An exemplary fragment 300 c maybe fragment F3 described in FIG. 1. An exemplary fragment header 306 amay be fragment header FH3 described in FIG. 1. An exemplary CRC field306 b may be CRC3 described in FIG. 1.

The APL 106 may generate fragment 300 d by combining fragment header 308a, CRC 308 b and fragment payload 308 c. An exemplary fragment 300 d maybe fragment FN described in FIG. 1. The APL 106 may generate fragment300 e by combining fragment header 318 a, CRC 318 b and fragment payload220 d. An exemplary fragment 300 e may be fragment FM described in FIG.1.

Additional fragments may be generated, for example, a fragment maycomprise fragment header 312 a, CRC field 312 b, and fragment payload312 c, another fragment may comprise fragment header 314 a, CRC field314 b, and fragment payload 314 c and another fragment may comprisefragment header 316 a; CRC field 316 b, and fragment payload 316 c.

In an exemplary embodiment of the invention, the APL 106 may sendfragment 300 a to PCS 108 a, fragment 300 b to PCS 108 b, fragment 300 cto a PCS 338 a, and fragments 300 d and 300 e to PCS 108 c.

FIG. 4 is a diagram of an exemplary fragment header for physical layeraggregation, in accordance with an embodiment of the invention.Referring to FIG. 4, there is shown a fragment header 400. The fragmentheader 400 may comprise a sequence number field 402 a, a start of frame(SOF) field 402 b and an end of frame (SOF) field 402 c. An exemplaryfragment header 400 may comprise fragment header FH1 described inFIG. 1. An exemplary sequence number field 402 a may be the sequencenumber <F1> described in FIG. 1. The SOF field 402 b may comprise anindication, SOF=1, that the associated fragment payload contains thefirst fragment in a packet. A value SOF=0 may indicate that theassociated fragment payload may not contain the first fragment in thepacket. The EOF field 402 c may comprise an indication, EOF=1, that theassociated fragment payload contains the last fragment in a packet. Avalue EOF=0 may indicate that the associated fragment payload may notcontain the last fragment in the packet.

FIG. 5 is a diagram of exemplary integrated circuit chip sets forphysical layer aggregation, in accordance with an embodiment of theinvention. Referring to FIG. 5, there is shown a switch integratedcircuit (IC) chip 500 a, a PHY layer IC chip 500 b, a switch IC chip 550a, a PHY layer IC chip 500 b, and a plurality of optical fibers 522 aand 522 b. The switch IC chips 500 a and 550 a may enable DLL relatedswitching functions, such as bridging. The PHY layer IC chips 500 b and550 b may enable PHY layer related functions, such as transmittingand/or receiving signals via one or more physical links. The opticalfibers 522 a and/or 522 b may be multi-wavelength fibers, which may beutilized for wide wavelength division multiplexing (WWDM), for example.

The switch IC chip 500 a may comprise a MAC 502, a reconciliationsublayer 504, an APL 506. The reconciliation sublayer 504 may representa protocol entity, which may provide a logical interface between the MAC502 and the APL 506.

The PHY layer IC chip 500 b may comprise one or more PCS instances 508a, 508 b, . . . , and 508 c, one or more PMA instances 510 a, 510 b, . .. , and 510 c, one or more PMD instances 512 a, 512 b, . . . , and 512c, and an optical multiplexer and demultiplexer (MUX/DeMUX) 520. In asource networking device, the optical MUX/DeMUX 520 may interface with aplurality of PMD instances 512 a, 512 b, . . . , and 512 c, wherein eachPMD instance may generate optical signals of different wavelengths. Theoptical MUX/DeMUX may combine the optical signals to generate acomposite optical signal comprising a plurality of differentwavelengths. The composite optical signal may then be transmitted viathe optical fiber 522 b. In a destination networking device, the opticalMUX/DeMUX 520 may receive a composite optical signal via the opticalfiber 522 a. The optical MUX/DeMUX 520 may filter the composite opticalsignal to generate a plurality of optical signals, wherein each opticalsignal may comprise distinct wavelengths. The optical MUX/DeMUX 520 maysend each of the plurality of generated optical signals to a PMDinstance selected from the plurality of PMD instances 512 a, 512 b, . .. , and 512 c.

In operation, a single switch IC chip 500 a may be communicativelycoupled to one or more PHY layer IC chips 500 b. Similarly, a singleswitch IC chip 550 a may be communicatively coupled to one or more PHYlayer IC chips 550 b.

As may be seen in FIG. 5, the location of the APL 506 may allowflexibility when implementing protocol stacks in IC chips. In anexemplary embodiment of the invention, the APL 506 may be located withinthe switch IC chip 500 a. In another exemplary embodiment of theinvention, the APL 506 may be located within the PHY layer IC chip 550b.

FIG. 6 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII, in accordance with an embodiment of theinvention. Referring to FIG. 6, there is shown a MAC 502, reconciliationsublayer 504, APL 506, a plurality of PCS instances 508 a, 508 b, . . ., and 508 c, a plurality of PMA instances 510 a, 510 b, . . . , and 510c, a plurality of PMD instances 512 a, 512 b, . . . , and 512 c, anoptical MUX/DeMUX 520, and a plurality of optical fibers 522 a and 522b.

As shown in FIG. 6, the APL 506 may be utilized in conjunction with the10G media independent interface (XGMII). As shown in FIG. 6, the XGMIImay provide an interface between the APL 506 and each PCS instance 508a, 508 b, . . . , and 508 c. Thus, in various embodiments of theinvention the APL 506 may be utilized with 10G Ethernet protocol stacks,which utilize the XGMII.

FIG. 7 is a diagram of an exemplary protocol stack for physical layeraggregation using an XAUI, in accordance with an embodiment of theinvention. Referring to FIG. 7, there is shown a MAC 502, reconciliationsublayer 504, APL 506, a plurality of XGMII extender sublayer (XGXS)instances 702 a, 702 b, . . . , and 702 c, and 704 a, 704 b, . . . , and704 c, a plurality of PCS instances 508 a, 508 b, . . . , and 508 c, aplurality of PMA instances 510 a, 510 b, . . . , and 510 c, a pluralityof PMD instances 512 a, 512 b, . . . , and 512 c, an optical MUX/DeMUX520, and a plurality of optical fibers 522 a and 522 b.

As shown in FIG. 7, the APL 506 may be utilized in conjunction with the10G extended attachment unit interface (XAUI). As shown in FIG. 7, theAPL 506 may interface with XGXS instance 702 a, 702 b, . . . , and 702c. The XAUI may interface with each XGXS instance 702 a, 702 b, . . . ,and 702 c, and each corresponding XGXS instance 704 a, 704 b, . . . ,and 704 c. Each XGXS instance 704 a, 704 b, . . . , and 704 c mayinterface with each corresponding PCS instance 508 a, 508 b, . . . , and508 c. Thus, in various embodiments of the invention the APL 506 may beutilized with 10G Ethernet protocol stacks, which utilize the XAUI.

FIG. 8 is a diagram of an exemplary protocol stack for physical layeraggregation with multi-conductor ribbon cable, in accordance with anembodiment of the invention. Referring to FIG. 8, there is shown a MAC502, reconciliation sublayer 504, APL 506, a plurality of PCS instances508 a, 508 b, . . . , and 508 c, a plurality of PMA instances 510 a, 510b, . . . , and 510 c, a plurality of PMD instances 512 a, 512 b, . . . ,and 512 c, and a plurality of physical links 802 a, 802 b, 804 a, 804 b,. . . , 806 a and 806 b.

FIG. 8 illustrates an exemplary embodiment of the invention in which thephysical links may be contained in a multi-conductor ribbon cable. Invarious embodiments of the invention, the plurality of physical links802 a, 802 b, 804 a, 804 b, . . . , 806 a and 806 b may be containedwithin a multi-conductor ribbon cable 812.

FIG. 9 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII with 10GBase-T, in accordance with anembodiment of the invention. Referring to FIG. 9, there is shown a MAC502, reconciliation sublayer 504, APL 506, a plurality of PCS instances508 a, 508 b, . . . , and 508 c, a plurality of PMA instances 510 a, 510b, . . . , and 510 c, a plurality of auto negotiation instances 902 a,902 b, . . . , and 902 c, and a plurality of physical links 904 a, 904b, 906 a, 906 b, . . . , 908 a and 908 b. As shown in FIG. 9, the XGMIImay provide an interface between the APL 506 and each PCS instance 508a, 508 b, . . . , and 508 c. The physical links 904 a, 904 b, 906 a, 906b, . . . , 908 a and 908 b may comprise shielded and/or unshieldedtwisted pair cables. Each auto negotiation instance 902 a, 902 b, . . ., and 902 c may enable a source networking device to negotiate with apeer auto negotiation instance in a destination networking device todetermine capabilities, such as data transfer rate, for communicationvia the connecting physical links.

FIG. 10 is a diagram of an exemplary protocol stack for physical layeraggregation using an XGMII with 10GBase-CX4, in accordance with anembodiment of the invention. Referring to FIG. 10, there is shown a MAC502, reconciliation sublayer 504, APL 506, a plurality of 10GBASE-X PCSinstances 1002 a, 1002 b, . . . , and 1002 c, a plurality of PMAinstances 510 a, 510 b, . . . , and 510 c, a plurality of PMD instances512 a, 512 b, . . . , and 512 c, and a plurality of physical links 1004a, 1004 b, 1006 a, 1006 b, 1008 a and 1008 b. As shown in FIG. 10, theXGMII may provide an interface between the APL 506 and each 10GBASE-XPCS instance 1002 a, 1002 b, . . . , and 1002 c. The physical links 1004a, 1004 b, 1006 a, 1006 b, . . . , 1008 a and 1008 b may compriseInfiniBand cables, for example. Each 10GBASE-X PCS instance 1002 a, 1002b, . . . , and 1002 c may enable a binary data to line code encodingand/or decoding suitable for 10GBASE-CX4 physical links.

FIG. 11 is a flowchart illustrating exemplary steps for transmittingpackets for physical layer aggregation, in accordance with an embodimentof the invention. Referring to FIG. 11, in step 1102, the APL layer 106may receive a packet from a DLL protocol entity, for example, from theMAC layer 104. In step 1104, the APL 106 may generate a plurality offragment payloads. In step 1106, the APL 106 may generate acorresponding plurality of fragment headers. A CRC field may begenerated corresponding to each fragment header. In step 1108, the APL106 may combine corresponding fragment headers, CRC fields, and fragmentpayloads to generate a plurality of fragments. In step 1110, the APL1110 may distribute the fragments to a plurality of PHY layer protocolinstances (for example, the plurality of PCS instances 108 a, 108 b, . .. , and 108 c) such that the fragments may be transmitted via aplurality of physical links 142 a, 144 a, . . . , and 146 a associatedwith a logical link 140.

FIG. 12 is a flowchart illustrating exemplary steps for receivingfragments for physical layer aggregation, in accordance with anembodiment of the invention. Referring to FIG. 12, in step 1202, the APL126 may receive a first fragment associated with a packet. The firstfragment may be identified by the SOF=1 field in the fragment header. Instep 1204, the APL 126 may receive additional fragments associated withthe packet. The APL 126 may receive fragments one or more PHY layerprotocol instances, for example, via the plurality of PCS instances 128a, 128 b, . . . , and 128 c. In step 1206, the APL 126 may inspect theCRC field in each received fragment. In step 1208, the APL 126 maydetect and/or correct binary errors in the corresponding fragment headerfield. In step 1210, the APL 126 may receive a last fragment associatedwith the packet. The last fragment may be identified by the EOF=1 fieldin the fragment header. In step 1212, the APL 126 may determine thateach fragment associated with the packet has been received based on thesequence number fields in each of the received fragments. While the APL126 may not receive the fragments in the order that they may have beentransmitted by the APL 106, the APL 126 may utilize the sequence numbersin the received fragments to rearrange the fragments to reflect theorder in which they were transmitted by the APL 106. In step 1214, theAPL 126 may extract the fragment payloads from each of the reorderedfragments. In step 1216, the APL 126 may assemble a received packetbased on the fragment payloads. The APL 126 may send the assembledpacket to a DLL protocol entity, for example, to the MAC 124.

Aspects of a system for physical layer aggregation may include one ormore switch ICs 500 a and/or physical (PHY) layer ICs 550 b that enablereception of data packets via a medium access control (MAC) layerprotocol entity. Each of the received data packets may be fragmentedinto a plurality of fragment payloads. Each of the plurality of fragmentpayloads may be sent to a PHY layer protocol entity instance a physicallayer protocol entity instance selected from a plurality of physicallayer protocol entity instances. The plurality of fragment payloads maybe transmitted via a plurality of physical links corresponding to atleast a portion of the plurality of physical layer protocol entityinstances. The plurality of physical links may be associated with asingle logical link. A fragment header may be generated for each of theplurality of fragment payloads. The fragment header may contain asequence number. The fragment header may contain an indication that thecorresponding fragment payload contains a first fragment or lastfragment from the received data packet. An error check field may begenerated based on the fragment header. A fragment may be generated bycombining a fragment header, error check field and correspondingfragment payload. Each fragment payload may be encapsulated in afragment when sending the fragment payload to a PHY layer protocolinstance.

Accordingly, the present invention may be realized in hardware,software, or a combination of hardware and software. The presentinvention may be realized in a centralized fashion in at least onecomputer system, or in a distributed fashion where different elementsare spread across several interconnected computer systems. Any kind ofcomputer system or other apparatus adapted for carrying out the methodsdescribed herein is suited. A typical combination of hardware andsoftware may be a general-purpose computer system with a computerprogram that, when being loaded and executed, controls the computersystem such that it carries out the methods described herein.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

While the present invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiment disclosed, but that the present invention willinclude all embodiments falling within the scope of the appended claims.

What is claimed is:
 1. A system comprising: one or more circuits for usein a network device, a first portion of said one or more circuits beingoperable to implement media access control (MAC) functions, a secondportion of said one or more circuits being operable to perform physicallayer aggregation, and a third portion of said one or more circuitsbeing operable to perform physical-layer functions for communicatingover a plurality of physical links, wherein: said first portion of saidone or more circuits is operable to encapsulate data into a packetcomprising a preamble and convey said packet to said second portion ofsaid one or more circuits; said second portion of said one or morecircuits is operable to fragment said packet into a plurality offragment payloads and convey each of said fragment payloads to saidthird portion of said one or more circuits, wherein at least one of saidplurality of fragment payloads comprises a preamble having each bitsequentially copied from said preamble of said packet; and said thirdportion of said one or more circuits is operable to add a header to eachof said plurality of fragment payloads to generate a correspondingplurality of fragments, and send said plurality of fragments over one ormore of said plurality of physical links.
 2. The system according toclaim 1, wherein said at least one of said plurality of fragmentpayloads comprises said preamble of said packet.
 3. The system accordingto claim 1, wherein said plurality of physical links is associated witha single logical link.
 4. The system according to claim 1, wherein saidone or more circuits enable generation of a sequence number within eachsaid header.
 5. The system according to claim 1, wherein said one ormore circuits enable generation of an indication within said header whena corresponding one of said plurality of fragment payloads comprises afirst fragment from said packet.
 6. The system according to claim 1,wherein said one or more circuits enable generation of an indicationwithin said header when a corresponding one of said plurality offragment payloads comprises a last fragment from said packet.
 7. Thesystem according to claim 1, wherein said one or more circuits enablegeneration of an error check field based on said header.
 8. A method forcommunication in a data communication system, the method comprising:performing by one or more circuits of a networking device: receiving,from a first portion of said one or more circuits, data encapsulatedinto a packet comprising a preamble; fragmenting said packet into aplurality of fragment payloads utilizing a second portion of said one ormore circuits; and conveying each of said plurality of fragment payloadsto a third portion of said one or more circuits, wherein at least one ofsaid plurality of fragment payloads comprises a preamble having each hitsequentially copied from said preamble of said packet.
 9. The methodaccording to claim 8, wherein said at least one of said plurality offragment payloads comprises said preamble of said packet.
 10. The methodaccording to claim 8 further comprising: adding a header to each of saidplurality of fragment payloads to generate a corresponding plurality offragments utilizing said third portion of said one or more circuits; andsending said corresponding plurality of fragments over one or more of aplurality of physical links.
 11. The method according to claim 10,wherein said plurality of physical links is associated with a singlelogical link.
 12. The method according to claim 10, wherein said thirdportion of said one or more circuits enables generation of a sequencenumber within each said header.
 13. The method according to claim 10,wherein said third portion of said one or more circuits enablesgeneration of an indication within said header when a corresponding oneof said plurality of fragment payloads comprises a first fragment fromsaid packet.
 14. The method according to claim 10, wherein said thirdportion of said one or more circuits enables generation of an indicationwithin said header when a corresponding one of said plurality offragment payloads comprises a last fragment from said packet.
 15. Acomputer system having stored thereon, a computer program having atleast one code section being executable to perform: receiving, from afirst portion of one or more circuits of said computer system, dataencapsulated into a packet comprising a preamble; fragmenting saidpacket into a plurality of fragment payloads utilizing a second portionof said one or more circuits; and conveying each of said plurality offragment payloads to a third portion of said one or more circuits,wherein at least one of said plurality of fragment payloads comprises apreamble having each bit sequentially copied from said preamble of saidpacket.
 16. The computer system according to claim 15, wherein said atleast one of said plurality of fragment payloads comprises saidpreamble.
 17. The computer system according to claim 15, wherein said atleast one code section being executable to further perform: adding aheader to each of said plurality of fragment payloads to generate acorresponding plurality of fragments; and sending said correspondingplurality of fragments over one or more of a plurality of physicallinks.
 18. The computer system according to claim 17, wherein saidplurality of physical links is associated with a single logical link.19. The computer system according to claim 17, wherein said at least onecode section is executable to further enable generation of a sequencenumber within each said header.
 20. The computer system according toclaim 17, wherein said at least one code section is executable tofurther enable generation of an indication within said header when acorresponding one of said plurality of fragment payloads comprises afirst fragment from said packet.
 21. The system of claim 1, wherein saidpreamble of said packet is not removed before fragmenting said packetinto said plurality of fragment payloads.
 22. The method of claim 8,wherein said preamble of said packet is not removed before saidfragmenting said packet into said plurality of fragment payloads. 23.The computer system according to claim 15, wherein said preamble of saidpacket is not removed before said fragmenting said packet into saidplurality of fragment payloads.
 24. The system of claim 1, wherein afirst one of said plurality of fragments begins with said preamble ofsaid packet.
 25. The method of claim 8, wherein a first one of saidplurality of fragments begins with said preamble of said packet.
 26. Thecomputer system of claim 15, wherein a first one of said plurality offragments begins with said preamble of said packet.